Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$18.63	11.172%	$20.7113	$20.71	$20.70	$20.70
Purchase #2	$217.50	6.510%	$231.6593	$231.66	$231.65	$231.70
Purchase #3	$197.78	12.338%	$222.1821	$222.18	$222.20	$222.20
Purchase #4	$239.80	7.544%	$257.8905	$257.89	$257.90	$257.90
Purchase #5	$127.55	3.736%	$132.3153	$132.32	$132.30	$132.30
Purchase #6	$49.56	11.158%	$55.0899	$55.09	$55.10	$55.10
Purchase #7	$65.55	10.594%	$72.4944	$72.49	$72.50	$72.50
7 purchase totals =	$916.37		$992.3428	$992.34	$992.35	$992.40